This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We are investigating the usage of Raman spectroscopy to guide stereotactic core needle biopsies of the breast for suspicious microcalcifications discovered at screening mammography. Microcalcifications are deposits of calcium mineral salts within breast tissue that mammographically localize the most clinically significant abnormality and are, therefore, a target for subsequent needle biopsy. Raman spectroscopy is exquisitely sensitive to the presence of calcium-containing minerals, and thus can be used to detect and localize microcalcifications in the breast. This can be done in vivo, in real-time, in a non-destructive manner, via optical fiber probes that are compatible with existing needle biopsy devices. The side-viewing Raman fiber optic probe provides capability of utilizing the excitation light from Raman source and delivering to and collecting the light from the breast tissue while the probe inserted into needle device. The probe is designed to fit into 9 gauge needle device most commonly used during stereotactic core needle biopsies. Similar to the front-viewing Raman probe that has been successfully used in the in vivo and ex vivo clinical studies, the side-viewing probe incorporate excitation and emission filters with coatings to suppress fiber background and enable efficient extraction of the Raman signal.